Understanding the Outrunner Motor Numbering System

Each motor has a 4 to 6 digit numbering system. For example: 2208/34. The first two numbers (22) represent the diameter of the stator (the fixed part in the middle of the motor) in millimeters. The second two numbers (08) represent the length of magnets (attached to the rotating case) in millimeters. The third set of two numbers (34) represents the number of wire winds, also called turns. There is usually a Kv rating given by the manufacture of the motor. Kv is basically how many revolutions per minute the motor will turn per volt at no load.

When comparing the motors within any series (2208, 2212, etc.) there are several characteristics that you will notice. Motors with higher winds spin slower for every volt of electricity applied, they have a lower Kv (RPM/V). They spin a larger propeller at slower speeds and at a lower current than low turn motors. Motors with lower winds spin faster for every volt of electricity applied, they have a higher Kv (RPM/V). They spin a smaller propeller at higher speeds and at a higher current than high turn motors.

To determine the motor for your model: analyze the character of your airplane, is it sleek and fast, or a slower plane with a lot of drag? For the high speed airplane a low turn motor that spins a small prop fast would be the right choice. For a Trainer or Biplane with a lot more drag, a high turn motor that can spin a much larger prop and produce a lot of thrust at low speed is what you want